2. DRUG ANTAGONISM
One drug or inhibits action of another drug
i.e
Effect of A + B < Effect of drug A +
Effect of drug B
3. Types of Antagonism
a) Physical antagonism
b) Chemical antagonism
c) Physiological/functional
antagonism
d) Pharmacological antagonism
4. A) Physical Antagonism
Based on physical property of drugs,
e.g. charcoal (adsorb alkaloid) in alkaloidal
poisoning
5. B) Chemical Antagonism
A type of antagonism where a drug
counters the effect of another by simple
chemical reaction / neutralization(not
binding to the receptor)
e.g. Calcium sodium edetate form insoluble
complexes with arsenic / lead
6. C) Functional Antagonism
(Physiological Antagonism)
Opposite effects of two drugs
on same function
Two drugs act on two diff. types of
receptors & antagonize action of each
other
e.g. Glucagon and insulin on blood sugar
level
9. 1.Same receptor by forming Weak
bonds
2.Maximal response is concentration
dependent
3.The effect of antagonist can be
overcome by increasing the
concentration of agonist
4. Parallel rightward shift of DRC
COMPETITIVE Reversible
ANTAGONISM
11. COMPETITIVE Irreversible
ANTAGONISM
1. Have affinity for the same receptor sites
and bind in an irreversible manner by
covalent bond
2. Effects cannot be overcome even by
increasing the concentration of the
agonist
3. LDR curves of agonist would show
reduced efficacy but altered potency
e.g. Dibenamine and NE at α1 adrenoceptors
13. i. Binds to site other than the agonist
site
ii. Prevent the receptor activation by
the agonist
e.g. Flumazenil by binding to BZD site
antagonises the effects of BZD by
preventing the binding of GABA to
GABAA receptor
Cont……
